Time-delay signal-repeater system



2 Sheets-Sheet 1 March 18, 1958 c. J. HlRscH TIME DELAY SIGNAL-REFETER SYSTEM Filed July 28,- 19755 March 18, 1958 c.; HIRSCH TIME DELAY SIGNALTREPEATER SYSTEM ,f

Fglled July 28, 1953 lmwewd lvuuawd' O uu lvlwewd United States atent TIME-DELAY SIGNAL-REPEATER SYSTEM Charles J. Hirsch, Douglaston, N. Y., assigner to Hazeltine Research, Inc., Chicago, Ill., a corporation of Illinois Application July 28, 1953, Serial No. 370,749

Claims. (Cl. Z50- 27) General This invention relates to time-delay signal-repeater systems for signals of variable magnitude.

Time-delay signal-repeater systems have particular utility in moving-target indicators which display indications of moving targets to the fairly complete exclusion of stationary targets. Some moving-target indicators provide desired displays by utilizing cancellation circuits which cause cancellation of pulses representative of stationary targets during successive repetition periods while pulses representative of moving targets during successive repetition periods develop resultant pulses for display. To eect cancellation of pulses representative of stationary targets during successive repetition periods, the pulses derived during a lirst repetition period may be delayed for an interval of one repetition period and then subtracted from pulses derived during the following repetition period.

It has heretofore been proposed to provide desired time delays of variable-magnitude signals, such as pulses representative of targets, by means of time-delay lines of conventional construction. Many types of time-delay lines, however, do not faithfully reproduce signals of variable magnitude translated thereby because of, for example, signal reections from the boundaries of the time-delay lines, pass-band limitations, and signal reflections within the time-delay lines caused by inhomogeneity of some time-delay wave-propagating materials.

It is an object of the present invention, therefore, to provide a new and improved time-delay signal-repeater system for signals of variable magnitude which avoids one or more of the above-mentioned disadvantages and limitations of such systems heretofore proposed.

It is another object of the invention to provide a new and improved time-delay signal-repeater system for signals of variable magnitude which faithfully reproduces variable-magnitude signals translated thereby.

In accordance with a particular form of the invention, a time-delay signal-repeater system for signals of variable magnitude comprises circuit means for supplying a variable-magnitude signal and circuit means for supplying a periodic signal. The system also includes circuit means coupled to the aforementioned supply circuit means for developing at times determined by the relative magnitudes of the variable-magnitude and periodic signals pulses time-modulated in accordance with the magnitude variations of the variable-magnitude signal. The signal-repeater system also includes timedelay pulse-translating circuit means coupled to the pulsedeveloping circuit means for translating the aforesaid time-modulated pulses with a predetermined time-delay interval during translation. The signal-repeater system also includes circuit means coupled to the time-delay circuit means and to the periodic-signal-supply circuit means for deriving at times determined by the aforesaid delayed a variable-magnitude signal.

senting a time-delay signal-repeater system embodyingY the present invention, and

Fig. 2 is a graph representing various signals developed by the signal-repeater system.

Description of signal-repeater system Referring now more particularly to Fig. 1 of the drawings, a time-delay signal-repeater system for signals of variable magnitude, constructed in accordance with the invention, comprises circuit means 10 for supplying The supply circuit 10 may, for example, be the receiver unit of a moving-target indicator for supplying video-frequency pulses which represent moving or stationary targets.

'5 The signal-repeater system'also includes circuit means for supplying one or more like periodic signals comprising, for example, a sinusoidal-signal generator 11 of conventional construction for developing a sinusoidal signal preferably having a peak-to-peak amplitude greater than the magnitude variations of the variable-magnitude signal supplied by the circuit 10 and having a repetition frequency offor example, 2 megacycles and preferably at least double the highest frequency component of the variable-magnitude signal.

-There is also provided circuit means coupled to the supply circuits 1t) and l for developing at times determined by the relative magnitudes of the variable magnitude and periodic signals pulses time-modulated in accordance with the magnitude variations of the variablemagnitude signal. More particularly, this circuit means comprises signal-comparing circuit means 12 for derivino time-modulated first pulses from the periodic signal supplied by the generator 11 at times when the variablernagnitude and periodic signals have substantially equal magnitudes. The signal-comparing circuit means 12 includes a diode 13 having its anode 13a coupled to the generator 11 through a butler repeater 14 of conventional construction and which may, for example, have unity gain. Cathode 13b of the diode 13 is connected to the variable-magnitude signal-supply circuit 10. The signal-comparing circuit means 12 also includes an output-signal resistor 15 coupled between the variablemagnitude signal-supply circuit 10 and circuit means including an amplifier and limiter 16 of conventional construction for developing time-modulated second pulses representative of the time-modulated first pulses mentioned above.

` The amplifier and limiter 16 is coupled through a differentiating circuit 17 of a conventional type to one input circuit of a modulator 13 also of conventional construction and responsive to positive and negative modulating pulses applied thereto, A radio-frequency oscillator 19 having an operating frequency of, for example, 50 megacycles is connected to another input circuit of the modulator 18 for developing in the output circuit of the modulator the aforementioned second pulses or bursts of radiofrequency energy.

The signal-repeater system also includes time-delay pulse-translating circuit means comprising, for example,

a pair of time-delay lines 20 and 21 preferably having Patented Mar.` 1s, fissa l Y. 3 l substantially equal time-delay characteristics Vfor translating the time-modulated pulses, ordinarily subject to amplitude degradation, with a'predetermined time-delay interval during translation which preferably is substantially equal to an integral multiple of one-half the ,periodV Vof the 'periodic signal supplied 'bythe generator-'11.

for deriving/thev modulation componeutsof the pulssfapplied thereto by time-delay linesil and The detector 24 is coupled"toanamplii'erand limiter '27 of conventional: constructionl forV ampliicationand amplitude-limiting purposesr .Y n 1 K u There isalsocoupled to the time-delaycircu1t means `20,72llfand to the periodic signal-supply circuit 11 circuit means for; deriving at times determined Yby the delayed time-nodulated pulses periodic-.signal samples representa-v tive of Vthe variable-magnitude' signal delayed by the above-mentioned predetermined interval.` YMore particularly, thisV ycircuitmeans. comprises ar'norrnally open switch-circuit means, for example, a normally noncon-v ductive `diode-bridge.'network 29 which is closed at times determinedby they delayed modulated pulses. The arms of the bridgenetwork include tubesvSS-SS, inclusive, normallybiasedt cutoi Yby a source of potential, such. as battery '39, included in a diagonal branchof the network. 29.` Thev amplifier' and limiter 27 is coupled to the diagonal branchkof the bridgeY network for supplying delayed tim'emodul'ated pulses to render the bridge network conductive at: times determined thereby.

Aniupu't terminal 29a ofthe bridge network 29 is coupledv tothe output circuit of the generator 11 and an output Vterminal 29b isV coupledY to` a low-pass filter network A3,0,for opening and closing the circuit connection betweenvthe generator 11 and the network 30. The net work 30 preferably has a cutot frequency between the highest yfrequency `component of the variable-magnitude signal-and the repetition frequency of the periodic signal suppliedby the generator ,'11 for attenuating frequency componentsV of the periodicfsignal samples above the cutoff frequency faithfully to Iepeattheyvariablemagnitude signal. In particular, the low-pass filter network 30 comprises shunt condensersl and-32 anda series inductor 33V coupled to the input circuit of a delayed signal-utilizing device 34 which may, for example,'be the plan-position indicator unit of: a 'moving-target indicator.

The units represented schematically may individually be of conventional construction and operation and a detailed explanation of theindivid'ual internal operations thereof is deemed unnecessary herein. Y

Operation Vof signal-repeater system Considering now the operation of the Fig. 1 repeater system Vwith reference to Fig. 2, ythe generator 11 supplies a `continuous sinusoidal signal which is repeated by Ythe bulfe'r repeater- 14 and applied to the signal-comparing means 12. Curve A ofFig. 2 represents the output signal of the repeater 14 at `the terminal thereof connected to theianode 13a of the diode 13 relativeto the terminal connected to the resistor 175. n

The variable-magnitude, signal-supply circuit 1,0 sup-Y plies at the terminal thereof connected to -the cathode .13bl of the diode 13 relative to the terminal connected tothe resistor 15 a signals represented, lfor example, vby curve B and comprising,.video-frequency pulses representing tar-1 gets. During intervals such as lQ--zl whenthesnusoidel gesmeer- 'f A signal represented by curve A has a 'morepflsitive magni-v A During the interveningintervals, such as t1-t2, ,when the magnitude of the signal representedy by 'curve 1B' is less posi...v Y curve A, thek diode 113- is nonconductlive andlno pulscsgare developed. across the resistor 15. Since the pulses developed aerosstheresistor 15a-nd representedby lcurve C 15V occur during intervals when the diode 13 conducts, the pulses are individuallyinitiatedeand' terminated at times when the sinusoidal and variable-magnitude signals have substantially equal magnitudes.V Y

The pulses developed across the resistor 15 are applied to the amplifier and limiter 16 which, by amplication and` amplitude-limiting, derives-pulses representedby curve D,.individually commencing and' terminating at times when Vthe sinusoidallsignal represented'by curve AA and the. variable-magnitude,signal represented byV curve Bhave-'equal magnitudes. YA sectionv of curve 'D within aY broken-line rectangle'ftlis drawnv to an expanded time scalev to represent Ythe 'slope of the leading and'trailing edges ofthe pulses of curve D.' Broken-line Aconstruc-A tion. of .the portions ofvcu'rve-'D and other curves withinV the rectangle 443 indicates that time intervals correspondd ingthereto havenot been lrepresentedy in their entirety. The time A.duration of the edges of the pulses of curve DV preferablynis insignificantv relative to the period of the sinusoidal'signallrepresented hycurveA, as indicated by theportion ofV CurvejD outside Jofthe vrectangle 4G. drawn Vto the same timescale as curve vFor example,

the duration-of the edges of curve D may-be short -com- Y Y offmicrosecond of the sinusoidal signa1ofcurve2A. Y Y 'd r The pulses representedV byrcurve D are applied by the pared witha-V period unit16 .to thel differentiating circuitV v17 which. derives negative ,and'p'ositive pulses, represented by curve Ey from the leading and trailingedges, respectively, of the pulses represented 'by-curve D. Thus, the derived positivefan'drnegative pulses occur at times when the sinusoidal and variable-magnitude signals represented by curves A and B, respectively, have substantially equalmagnitudes. Thederiied Vpositive-rand]negati-ve pulses represented by curvel-EY are, therefore,time-modulated in accordance with magnitude variations ofthe variable-magnitude signal represented by curve'l'B; A section of curve E within the rectangle this drawn tothe same expanded time scale a's the correspondingvsecti'on of curve D. Y

VThe pulsesderivedtbyfthedifferentiating circuit 17 are applied toV themodul'atori8 while a radio-frequency signal is applied thereto Vby the Voscillatore@V to develop Vin the output circuit of the modulator pulses or bursts of radioafrequency'enerrgy represented by curve'F and occur-v ring Vduring jthe intervals of tliepulses` represented by curve E and,thus,time4modulated in accordance with the magnitude variations Vofi'the variable-magnitude signal represented by curveil'. Two pulses of radio-frequency e energy represented by curve'F are drawnto' expanded time scale within the rectangle 4t) forfclarity.

The modulator l applies the pulses of radio-frequency Y delayy interval duringgtranslation equal, for example, Vto;

LOGO-.periodsgof fthe ,sinusoidalV signal. supplied by the generatorV l1' to provide a time delay of, -for examplelQtl; microseconds. vThe time-delay lines 20131151.21 Aeriiriarilcause amplitude degradation ofthe translated pulses due Y .han the magnitudev of'..t.hei.signal represented .by

aaai-,56a

to, for example, anyof the factors previously mentioned as' delay-line limitations. vHence the output pulses of the delay lines 20 and 21, represented by curve G, may, for example, be degraded as indicated by the expanded portionof curve G-within a broken-line rectangle 41. Broken-line construction of portions of the curves within rectangle 41 indicates that the time intervals corresponding thereto are not represented in their entirety.

The time-delay lines 20 and 21 apply the delayed timemodulated radio-frequency pulses to the detector 24 which derives the modulation components thereof, as represented by curve H of Fig. 2. A porton of curve H enclosed within the rectangle 41 and drawn to the same expanded time scale as the corresponding portion of curve G represents the derived modulation components in detail. The pulses represented by curve H are applied by the detector 24 to the amplifier and limiter 27 which, by usual operations of amplification and amplitude-limiting, develops substantially rectangular amplitude characteristics for the individual delayed time-modulated pulses, as represented by the portion of curve I drawn to expanded time scale within the rectangle 41.

The amplifier and limiter 27 supplies the pulses represented by curve I to the diode-bridge network 29, overcoming the bias supplied by the battery 39 and rendering the bridge network conductive during the intervals of the pulses. The sinusoidal-signal generator 11 also applies to the bridge network 29 the sinusoidal output signal thereof represented by curve J of Fig. 2. When the bridge network is conductive, current flows through the condenser 31 and the bridge network to the output circuit of the generator 11, charging the condenser 31 to the instantaneous magnitude value of the output signal of the generator 11. When the condenser 31 acquires a positive incremental charge, current Hows through diodes 36 and 37 and when the condenseracquires a negative incremental charge, current flows through diodes 35 and 38.

During the intervals between pulses represented by curve I, the condenser 31 maintains a substantially constant charge thereon until the next conductive interval of the bridge network 29. Accordingly, there is developed across the condenser 31 a signal represented by curve K which is representative of the variable-magnitude signal supplied by the circuit and represented by curve B. rl`he signal represented by curve K is delayed from the signal represented by curve B by a predetermined interval in accordance with the time-delay characteristic of the imc-delay lines 20 and 21. The low-pass iilter network 30 is eiective to derive for application to the delayed signal-utilizing device 34 a signal which is a more faithful reproduction of the variable-magnitude signal represented by curve B by attenuating in a conventional manner the high-frequency components of the signal represented by curve K above the cuto frequency of the lter network. l

Returning now to a further consideration of the switching operation of the relay switch element 23b accomplished by the timing circuit 22, the operation of the timing circuit is synchronized with the operation of the sinusoidalsignal generator 11 by the application of the sinusoidal output signal thereof to the timing circuit through the 90 phase-shifting network 25. Because of the 90 phase shift in the signal applied to the timing circuit 22, the timing circuit maintains the relay 23a in an energized condition during peak-to-peak magnitude excursions of one sense of the sinusoidal signal developed by the generator 11 and maintains the relay winding 23a in a de-energized condition during peak-to-peak magnitude excursions of the other sense. Accordingly, the relay switch. element 23b is in vone position during theoccurrence of bursts of radio-frequency energy corresponding to the positive pulses of curve E and is in a second position during the occurrence of bursts of radio-frequency energy crresponding to the negative pulses represented by curve E. Alternate connection of the delay lines 20 and 21 to the modulator 1S is useful in applications where the pulse-repetltion frequency is so high that a single delay line is incapable of translating all the output pulses of the modulator 18. For some applications, however, a single time-delay line will be capable of translating all the output pulses of the modulator 18 and, of course, time-delay line 20 or 21, the units 22, 25, the relay winding 23a and switch element 23b may then be eliminated and the modulator 18 may be directly connected to the remaining time-delay line.

From the foregoing description, it will be apparent that a time-delay signal-repeater system constructed in accordance with the invention has the advantage of faithfully reproducing a variable-magnitude signal translated thereby notwithstanding amplitude degradation caused during translation by one or more time-delay lines employed in the system. This advantage is provided because time-delay lines which may have poor signal-magnitudetranslation characteristics are utilized to translate timemodulation information which represents signal-magnitude information and may thereafter be converted to signalmagnitude information delayed by a predetermined interval.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A time-delay signal repeater system for signals of variable magnitude comprising: a circuit for supplying a variable-magnitude signal; a circuit for supplying a sinusoidal signal having a peak-to-peak amplitude greater than the magnitude variations of said variable-magnitude signal and having a frequency at least double the highest frequency component thereof; signal-comparing circuit means coupled to said circuits for deriving from said sinusoidal signal at times when said variable-magnitude and sinusoidal signals have substantially equal magnitudes first pulses time-modulated in accordance with the magnitude variations of said variable-magnitude signal;

circuit means coupled to said signal-comparing circuit means for developing time-modulated second pulses representative of said lirst pulses; a time-delay pulse-translating line coupled to said pulse-developing circuit means for translating said time-modulated second pulses with a predetermined time-delay interval during translation substantially equal to an integral multiple of one-half the period of said sinusoidal signal; and normally open switch circuit means coupled to said time-delay line and to said sinusoidal-signal-supply circuit and closed at times determined by said delayed time-modulated pulses for deriving samples of said sinusoidal signal representative of said variable-magnitude signal delayed by said predetermined interval.

2. A time-delay signal-repeater system for signals of variable magnitude comprising: circuit means for supplying a variable-magnitude signal; circuit means for supplying one or more like periodic signals; circuit means coupled to said supply-circuit means for developing at times determined by the relative magnitudes of said variable-magnitude and periodic signals pulses timemodulated in accordance with the magnitude variations of said variable-magnitude signal; time-delay pulsetranslating circuit means coupled to said pulse-developing circuit means for translating said time-modulated pulses with a predetermined time-delay interval during translation; and circuit means coupled to said time-delay circuit means and to said periodic-signal-supply circuit means for deriving at times determined by said delayed time-modulated pulses periodic-signal samples repre..-

Y 7 .s sentative. of said variable-magnitude; signaldelayed byV said predeterminedinterval.` Y Y j 1 jj K "L"l AQ ,time-delayA signal-repeater' system .for signals" ot'` variable' magnitude comprising: a circuit folsurpplyinga variable-magnitude signal;` a circuit.. for supplying a` periodic'signal; circui'tmeans coupled toV saidf'circuits fordesvelopingattimes/'determinedl by therelativefmagnitudes ofV saidV variable-magnitude and periodici-signals' 'pulsesy time=modulated in Vaccordance Witli 'themagnitude variations of saidA variable-rna'gnitudesignal; ztime-delaypulse; translating circuit means coupledto said puise-developing circuitmeans for translating' said time-modulatedfpulses With'V a, predetermined j time=de`layntervali during' translation; and circuitzmeans' coupled)V tof'saidv time-delayl circuit means and' tosaidperiodic=signa-supply*circuit for deriving at times Ydeterrnine'dby saidfY delayed timemodulated pulsesV samples of `sajd periodic signal represaidjpredeter'mined interval. l; Y t t Y Y Y .Y Y p 4. A time-delay signalirepeaterjsyste'm; for. slgnalsfof variablemagnitude comprising: a `circuit for'supplyinga variable-magnitude signal; a'circuit for 'supplying a'sinusoidal signal having a peak-to-peak amplitude greaterV than the magnitude variationsof said variable-magnitude signal; circuit means, coupled to said circuits fork developing at times4 determined by the relative magnitudes of saidivariable-magnitude and'sinusoidallsignals pulses timemodulatedin accordance with the ma'guitudetvariations of said variable-magnitude signal; time-delay pulse-trans-v lating circuit means coupledto said'pulse-developing,circuit meansV for translating said time-modulated pulses .with a. predetermined time-delay interval duringV translation; and circuitV means coupled to said time-delay circuit means and to` said sinusoidal-signal-supply; circuit forY deriving at timesjdeterminedV by, said delayed rtime-modulated pulses samplesV ofisaid sinusoidalY signal-representative of saidV variable-magnitude signal delayedby saidl predetermined interval.

' tion; and circuit means coupledV to said time-delay circuit means andto said sinusoidal-signal-supplyA circuit for deriving at times determined by saiddelayed time-modulated pulses samples of said sinusoidal signaLrepresentative-of said variable-magnitude signal delayed by said predetermined interval. Y Y Y 6. A time-delay signal-repeater system for signals of variable magnitude comprising: .a circuit for supplying a variable-magnitude signal; afcircuit for supplyinga periodic signal; signal-comparing circuit means coupled to said circuits for derivingV fromV said periodic signal at times when said variable-magnitude and periodic signals have Vsubstantially equal magnitudes rst pulses timemodulated in accordance with the magnitude variations of said;variablemagnitude signal; circuit means coupled to. said signal-comparing circuit means for; developing time-modulated second pulses representativesof said iirst pulses; time-delaypulse-translating circuit Ymeans 'coupled tosaid pulse-developing circuitmeans-tor;l translating said time-modulated second pulses with a predetermined Vtime-r delayl interval during translation; and circuit meansY coupled to saidtime-delay vcircuit me'ansand-toV Vsaid *periodicsignal-supply circuit Vforfderiving at-Itir'nes determined'by' sentative oLsaid variatile=magnitudesignal "delayed by.V Y

f esame-t" Y said Ydelayed Atiine-'nrodulated pulses; samples of s aid peri- Y odic signal representative"rofsaidvariable-niagmtudesignalj delayed by said .predetermined interval. r

7. -tirnedelay signalrrepeater systemY for signals o'f variable'l magnitude; comprising;Y a' circuit for supplying a variable-magnitudYsignal; a* Vcircuit""fc' 'r`'supplying a periodic' signahcircuit meansfcoupledto' 'said' circuitsgfor developingrat` times determined" byA the relative magnitudes: of saidVvarialjl'e-ma'gnitude` and periodic signals y pulses timelmodulatld.infactzordance with the'magnitude variations of said v'ariatale-miagnitu'de:signal; va time-delay pulse-translatingline"coupledltosaidSpulse-developing circuitAV means for; translating said time-modulated pulses with a` predetermined time-delay" intervalV during trans- 'lation' substantially yequalto anrntegral' multiple of onehalf thev .periodA of' saidLperiodic-signal; and circuit Ymeans coupled'to said time-delaycircuitfmeans and to said periodic-signal-'supply circuitfr deriving at times determined by said.delayed"time-modultedpulses samples of said periodicV signal representative of said Variable-magnitude Ytions of'said'variable-magnitude'signal; a pair of timedelay pulse-translating circuit means having substantiallyV equaltinie-dlay characteristics for translating 'saidA time-modulated'pulses with apredetermined time-delay intervalA during translation; ,switch-circuit means coupled'to said periodic signal-'supply circuit and operatively synchronized'th'erewith Vforaliernately coupling individual ones ,of saidpair ottime-delay.v circuitmeans to said pulse-developing circuit means; and circuit means-coupled to said .time-delay circuit .-mea-nsfand tofsaid Vperit odic-signal-supply. circuitrtontderiving at times determined by said delayeditinie-modulated. pulses samples t. of said periodic` signal representative of. said variablemagnitude signaldelayedfbyfsaid predetermined interval. 9.V A time-delay signal-repeater system for. signals of variable magnitudecomprising: a circuit for supplying a variable-magnitude.signal; a circuit for supplying a-perif odic signal; circuit. meansicoupled toy said. circuits for developing at timesdetermined by therelative magnitudes.

of said variable-magnitude and periodicV signals pulsesY time-modulatedin accordancewith. the magnitude variationsof said.variable-magnitude.:signal; time-delay pulsef translatingcircuit meanscoupled to said pulse-developing circuit means for translating said time-modulated pulses with aV predetermined. time-delayY interval during trans- Y lation;. andv normally open .switch-circuit means coupled to said time-delay circuit means and to said periodic-V signal-supr'ilyp circuitandclosed: atftimes determined by saiddelayed time-modulated-pulses for deriving samples of 'said periodic Ysignal representative of. saidV variablemagnitude signal .delayed by -said'predetermined interval.V 1Q; A time-.delay signal-repeater system for signals ofV variable magnitudecomprising: a. circuit for supplying a variable-magnitudessignal; a circuit for supplying aperiodicy signalhaving;afrepetition frequency at least double the-.highest frequencyjcomponent of'said variable-magnitude signaljcircuit means coupled' to said circuits for developing'at timesdetermined bythe relative magnitudes ofi said.variable.magnitude and! periodic signals pulses time-modulated iin-'accordance With vthe magnitude. varia- ,tions of 'sa-itl variable-magnitude' signal; time-delayy pulse-Y 1 translatingfcircuitmeans coupled"to'saidpulse-developing circuit i means fr-'translating said" time-modulated pulses with a' predetermined?time-delay, interval during translaf tion; circuit' means" coupled* to said' time-delay' circuit vmeans and e to" saidperiodi'clsignalsupply circuit for de" riving at times determined by said delayed time-modu- References Cited in the le of this patent lated pulses samples of said periodic signal representative of said Variable-magnitude signal delayed by said UNITED STATES PATENTS predetermined interval; and a 10W-pass lter network 2,405,876 Crosby Aug. 13, 1946 coupled to said signal-sample-deriving circuit means and 5 2,542,700 Peterson Feb. 20, 1951 having a cutoff frequency between said highest frequency 2,557,950 Deloraine June 26, 1951 component of said variable-magnitude signal and said 2,638,572 Goubau May 12, 1953 repetition frequency of said periodic signal for atteuuat- 2,666,136 Carpenter Ian. 12, 1954 ing frequency components of said samples above said 2,678,388 Loughlin May 11, 1954 cutot frequency faithfully to repeat said VariabIe-rnagni- 10 2,686,869 Bedford Aug. 17, 1954 tude signal. 

